Process for polymerizing monomers using a catalyst system comprising diarylethane, alpha-ketol and monocarboxylic acid



United States Patent 3,214,497 PRQCESS FUR PQLYlllERlZlNG MONOMERS US- INC A CATALYST SYSTEM CGMPRHSING Dil- ARYLETHANE, ALPHA-KETOL AND MONO. CARBOXYLIC ACID Alva E. Harris, Wilbralram, Mass, assignor to Monsanto Company, a corporation of Delaware No Drawing. Filed Feb. 5, 1963, Ser. No. 256,274 13 Claims. (Cl. 260--880) This invention relates to the polymerization of styrenetype monomers and more particularly relates to the use of a novel catalyst system in the polymerization of such monomers.

It is known that styrene-type monomers can be polymerized thermally or catalytically to prepare polymers having molecular weights and residual monomer contents which vary with certain reaction parameters, e.g., the catalyst concentration, the time and temperature of the reaction, etc. It is also known that the product normally has an undesirably high residual monomer content when the parameters of a mass polymerization process are controlled so as to prepare a molding-grade polystyrene, i.e., a polystyrene having a Staudinger average molecular weight in the range of about 40,000100,000.

As shown in US. Patent 2,675,362, certain catalysts make it possible to use a mass polymerization process in preparing molding-grade polystyrene having a residual monomer content as low as 0.350.5%, and the product has improved physical and molding properties because of the reduction in residual monomer content. It would obviously be desirable to find a catalyst capable of reducing the residual monomer content to even lower levels without otherwise causing degradation of the product because of (1) the greater improvement in the physical and molding properties of the polymer which could result from the greater reduction in residual monomer content and (2) the decreased likelihood of reaching undesirably high levels with the anomalously higher-thannormal residual monomer contents which are occasionally eencountered when styrene-type monomers are mass polymerized on a commercial scale.

An object of the invention is to provide a novel process for polymerizing styrene-type monomers.

Another object is to provide a process for polymerizing styrene-type monomers in the presence of a novel catalyst system.

A further object is to provide a mass process for polymerizing styrene-type monomers to moldable polymers containing a minimum amount of residual monomer.

These and other objects are attained by (l) dissolving a catalytic mixture of a 1,2-diarylethane, an alphaketol, and a monocarboxylic acid having a dissociation constant not higher than 1.0 at 25 C. in a polymerizable material comprising a monovinyl aromatic hydrocarbon and/or an ar-halo monovinyl aroma-tic hydrocarbon and (2) heating to polymerize the polymerizable material.

When desired, the catalyst mixture can also include a monomer-soluble peroxy compound having a half-life of at least 10 hours in benzene at 100 C. This optional ingredient is particularly apt to be desirable when the invention is applied to a mass polymerization process utilizing the time-temperature cycle which is hereinafter defined as the cycle which should be employed when the reaction is intended to produce a moldable polymer having a minimum residual monomer content.

The following examples are given to illustrate the invention and are not intended as a limitation thereof. In the reactions described in these examples (1) quantities mentioned are quantities .by weight unless otherwise specified, (2) the monovinyl aromatic monomers employed 3,214,4 9? Patented Oct. 26, 1965 as starting materials are commercially-supplied monomers containing 0.0010.00l5% t-butyl catechol and varying amounts of the impurities normally present in commercially-supplied styrene-type monomers, and (3) aliquots of the same monomer sample are polymerized in any series of reactions proposed for direct comparison of results.

EXAMPLE I Part A.Contr0l Dissolve 0.04 part of di-t-butyl peroxide and 0.28 part of stearic acid in parts of styrene. Purge the reaction vessel with nitrogen and heat at 90 C. for 24 hours to convert about 30% of the styrene to polymer. Then gradually raise the reaction temperature to C. over a period of 4.75 hours and maintain the temperature at 190 C. for an additional 4 hours. The product has a Staudinger average molecular weight in the range of 40,00100,000 and a residual monomer content of 1.37%.

Part B.-Contr0l Prepare two products by repeating Part A except for also dissolving, respectively, 0.05 part and 0.1 part of alpha-hydroxyacetophenone in the monomer. Each of the products has a Staudinger average molecular weight in .the range of 40,000l00,000 and a residual monomer content of 1.00%.

Part C.-Control Prepare four products by repeating Part A except for also dissolving respectively, 0.05 part, 0.1 part, 0.2 part, and 0.5. part of 1,2-diphenylethane in the monomer. The products have Staudinger average molecular weights in .the range of 40,000-100,000 and respective residual monomer contents of 1.30%, 1.30%, 1.32%, and 1.19%.

Part D Prepare eight products by repeating Part A except for also dissolving varying amounts of 1,2-diphenylethane and alpha-hydroxyacetophenone in the monomer. Each of the products has a Staudinger average molecular weight in the range of 40,000-100,000. The residual monomer contents of the products, together with the amounts of 1,2-diphenylethane (DPE) and alpha-hydroxyacetolphienone (HAP) employed in their preparation, are shown 1 e ow.

DPE HAP Residual Reactlon Number (parts) (parts) Monomer (percent) As demonstrated in the preceding example, the addition of both 1,2-diphenylethane and alpha-hydroxyacetophenone to a di-t-butyl peroxide/stearic acid catalyst systern can effect a 9497% decrease in the residual monomer content of the product, although the addition of 1,2-diphenylethane alone 'has substantially no etfect on residual monomer content and the addition of alpha-hydroxyacetophenone alone has a much smaller effect on residual monomer content. Similar results are observed when Example I is repeated except that:

(1) No di-t-butyl peroxide or other peroxy compound is employed,

( 2) The time-temperature cycle employed for the reaction is (a) 24 hours at 90 C., followed by 3.5 hours at 3 90-185" C., followed by 1 hour at 185 C., (b) 24 hours at 90 C., followed by 6.25 hours at 90-l85 C., followed by 1.5 hours at 185 C., or (c) 12 hours at 1l090 C., followed by 4.5 hours at 90190 C., followed by 3 hours at 190 C.,

(3) The 1,2-diphenylethane is replaced with 1,2-di(omethylphenyl)ethane, 1,2-di(p chlorophenyl)ethane, 1,2-di(2,5-dichlorophenyl)ethane, 1,2-di(p-t-butylphenyl)ethane, or 1,2-dinaphthylethane,

(4) The alpha-hydroxyacetophenone is replaced with acetoin or benzoin,

(5) The 0.28 part of stearic acid is replaced with 0.4 part of stearic acid, 0.1 part of benzoic acid, or 0.06 part of acetic acid, or

(6) The 100 parts of styrene are replaced with 100 parts of p-chlorostyrene, 100 parts of a mixture of o-, m, and p-methylstyrenes, a mixture of 85 parts of styrene and parts of acrylonitrile, a mixture of 80 parts of styrene and parts of methyl methacrylate, a mixture of 75 parts of styrene and parts of alphamethylstyrene, or a solution of 10 parts of a rubbery butadiene-styrene (75:25) copolymer in 100 parts of styrene.

EXAMPLE II Prepare two products by dissolving 0.04 part of di-tbutyl peroxide and, respectively, 0.05 part and 0.1 part of 1,2-diphenylethane in 100 parts of styrene and polymerizing and monomer by the procedure described in Example I. The products have Staudinger average molecular weights in the range of 40,000100,000 and respective residual monomer contents of 1.37% and 1.40%.

Part B Prepare two products by repeating Part A except for also dissolving 0.05 part of alpha-hydroxyacetophenone in the monomer. The products have Staudinger average molecular weights in the range of 40,000100,000 and respective residual monomer contents of 1.34% and 1.37%.

As shown in Example II, 1,2-diphenylethane and alphahydroxyacetophenone do not act synergistically in the absence of a stearic acid-type compound.

The process of the invention comprises (1) dissolving a catalyst mixture consisting of a 1,2-diarylethane, an alpha-ketol, a weak organic acid, and an optional peroxy compound in a polymerizable material comprising a styrene-type monomer and (2) heating to cause polymerization.

The 1,2-diarylethane employed in the practice of the invention is a compound corresponding to the formula:

wherein R and R represent aryl radicals, e.g., phenyl, alkylphenyl, alkoxyphenyl, halophenyl, naphthyl, alkylnaphthyl, halonaphthyl, biphenyl, etc. Exemplary of utilizable 1,2-diarylethanes are 1,2-diphenylethane; ar-alkyldiphenylethanes, such as the 1,2-di(o-, m-, and p-methylphenyl)ethanes, 1,2-di(p-ethylphenyl)ethane, 1,2-di(p-tbutylphenyl)ethane, 1-phenyl-2 p-methylphenylethane, etc.; ar-halodiphenylethanes, such as the 1,2-di(o-, m-, and p-chlorophenyl)ethanes, 1,2 di(p-bromophenyl)ethane, 1,2-di(2,5-dichlorophenyl)ethane, 1,2-di(2-ohloro-4-methylphenyl)ethane, etc.; ar-alkoxydiphenylethanes, such as 1,2 di(p-methoxyphenyl)ethane, etc.; 1,2 dinaphthylethane; ar-substituted dinaphthylethanes, such as the 1,2- di(ar-chloroand ar-methylnaphthyl)-ethanes, etc.; and mixtures thereof. Although, as demonstrated, these utilizable compounds can bear a plurality of ar-substituents, 1,2-diarylethanes having ar-substituents in all four of the ortho positions will not ordinarily be found effective in the practice of the invention except when they are used in conjunction with the more reactive 1,2-diarylethanes which are free of substituents in at least one of these ortho positions. The preferred 1,2-diarylethanes are those in which R and R of the above formula represent the same aryl radical; 1,2-diphenylethane is especially preferred.

The 1,2-diarylethane is employed in concentrations of 0.05-0.5%, preferably 0.05-0.1%, based on the weight of polymerizable material.

The alpha-ketol employed as a catalyst component can be any monomer-soluble compound containing the alpha-ketol grouping, e.i.

and is preferably a compound corresponding to the formula:

wherein R represents a hydrocarbon radical, R represents a substituent of the group consisting of hydrogen and a hydrocarbon radical, and R represents a substituent of the group consisting of hydrogen and a hydrocarbon radical. Suitable alpha-ketols include, e.g., aliphatic alpha-ketols such as hydroxyacetone, acetoin, propionoin, butyroin, isobutyroin, valeroin, hexamethylacetoin, capronoin, 3,8-dimethyldecan 5 one-6-ol, capryloin, nonyloin caprionoin, l,21-docosadien 11 one-l2-ol, 2,20-docosadiyn-ll-onc-lZ-ol, lauroin, myristoin, palmitoin, stearoin, etc.; alicyclic alpha ketols such as alpha hydroxycyclohexanone, alpha-hydroxycyclononanone, etc.; aromatic alpha-ketols such as benzoin, alpha-methylbenzoin, cyclohexoylphenylcarbinol, dodecahydrobenzoin, 2,2'-dichlorobenzoin, 3,3-dibromobenzoin, 4,4-diiodobenzoin, 4-chlorobenzoin, 3-methylbenzoin, 2,2'-di-methylbenzoin, 2,4,6- trimethylbenzoin, 4 isopropylbenzoin, naphthabenzoin, 2,2',6,6-tetramethylbenzoin, alpha-naphthoin, beta-naphthoin, 4,4'-diphenylbenzoin, etc.; and mixtures thereof.

The alpha-ketol is employed in concentrations of about 0.0010.5%, preferably 0.0010.1%, based on the weight of polymerizable material. The lower concentrations of alpha-ketol are ordinarily preferred becouse they permit better control of the reaction rate.

The weak organic acid employed as a catalyst component can be any monocarboxylic acid having a dissociation constant not higher than 1.0 10 at 25 C. Among the particularly suitable acids are acetic, hexanoic, benzoic, phenylacetic, isopropylbenzoic, and hexahydrobenzoic acids and, as a preferred embodiment of the invention, alkanoic acids containing 12-20 carbon atoms (i.e., lauric, tridecanoic, myristic, pentadecanoic, palmitic, margaric, stearic, nonadecanoic, and eicosanic acids). Stearic acid is especially preferred because of the brillance it imparts to the molded polymers.

The reaction mixture should contain at least 0.05% of the weak organic acid, based on the weight of polymerizable material, and usually contains not more than 1% of the acid. Within the range of 0.05-1% and at higher concentrations, variation in the concentration of a particular acid seems to have no substantial effect on the molecular weights and residual monomer contents of the polymers formed by the reaction, but it is usually preferred to avoid concentrations higher than 1% in order to avoid undue yellowing of the polymer. Ordinarily the reaction mixture will contain 0.1-0.6% of the acid.

The optional component of the catalyst mixture can be any monomer-soluble peroxy compound having a half-life of at least 10 hours in benzene at C. Utilizable peroxy compounds include, e.g., hydrogen peroxide, di-tbutyl diperphthalate, t-butyl peracetate, t-butyl perbenzoate, dicumyl peroxide, di-t-butyl peroxide, 2,5-dimethyl- 2,5-di(t-butylperoxy)hexane, 2,5-dimethyl-2,5-di(t-butylperoxy)hexyne 3,t butyl hydroperoxide, cumene hydroperoxide, p-methane hydroperoxide, cyclopentane hydroperoxide, diisopropylbenzene hydroperoxide, p t butylcumene hydroperoxide, pinane hydroperoxide, 2,5 dimethylhexane 2,5 dihydroperoxide, etc., and mixtures thereof.

The reaction mixture can contain up to 0.1% of the peroxy compound, based on the weight of polymerizable material. This optional component may be found desirable when a substantial amount of the polymerization is to be accomplished at temperatures at which such peroxy compounds are effective, e.g., when the process utilizes the time-temperature cycle hereinafter defined as the cycle to be employed in a mass process when the product is to be a moldable polymer containing a minimum amount of residual monomer. When included as a catalyst component, the peroxy compound is usually employed in concentrations of 0.01-0.1%, preferably 0.01-0.05%.

The catalyst mixtures of the invention are used in the polymerization of polymerizable materials comprising a monovinyl aromatic hydrocarbon and/or an ar-halo monovinyl aromatic hydrocarbon, e.g., styrene; vinyl naphthalene; ar-alkylstyrenes, such as o-, m-, and p-methylstyrenes ar-ethylstyrenes, etc.; o-chlorostyrene; p-bromostyrene; 2 chloro 4 methylstyrene, etc., and mixtures thereof. Such monovinyl aromatic monomers, as is well known, normally contain minor amounts of impurities formed as by-products of the monomer synthesis or accumulated during storage. Since the presence of these impurities appears to be more desirable than undesirable in the practice of the invention, they are not removed from the monomers prior to polymerization except when the particular application for which the product of the polymerization is intended requires the removal of one or more particular impurities known to contribute properties which would be undesirable in that application, e.g., excessive amounts of dissolved oxygen are removed when the application will not tolerate the degree of yellowness that would be contributed to the polymer by large amounts of oxygen.

The monovinyl aromatic monomer may constitute the only component of the polymerizable material or may be in admixture with lesser amounts of one or more copolymerizable monomers, such as acrylonitrile; methacrylonitrile; an alkyl methacrylate, e.g., the methyl, ethyl, propyl, and butyl methacrylates; the corresponding alkyl acrylates; alpha alkylstyrenes, e. g., alpha methylstyrene, alpha-ethylstyrene, alpha-methyl-p-methylstyrene, etc.

When desired, the polymerizable material can have a rubbery conjugated 1,3-diene polymer (e.g., natural rubber, polybutadiene, polyisoprene, copolymers of butadiene and/0r isoprene with lesser amounts of comonomers such as styrene, acrylonitrile, methyl methacrylate, etc.) dissolved therein, ordinarily in amounts of 1-25%, based on the weight of polymerizable material. Also, the reaction mixture can contain other optional ingredients such as plasticizers, mineral oils, stabilizers, etc.

The process of the invention is ordinarily conducted at temperatures in the range of about 90220 0., although the early stages of the polymerization can be conducted at lower temperatures, e.g., 75-90 C., if desired. As will be readily understood, the particular polymerization temperatures which are most desirably employed in the practice of the invention depend on the technique being used (e.g., a mass, suspension, batch, or continuous technique) and the molecular weight desired for the product. Methods of varying polymerization conditions to obtain a particular type of product are, of course, already well known.

A preferred embodiment of the invention is the use of the 1,2-diarylethane/alpha-ketol/weak organic acid catalyst systems in the mass polymerization of styrene-type monomers to moldable polymers having a minimum residual monomer content. In order for the product of this mass process to have the desired properties, a fairly specific time-temperature cycle should be employed. In the first stage of the reaction, polymerization is conducted at 75-125 C. for about 6-24 hours until -45% of 6 the monomer has been converted to polymer; in the second stage, the reaction temperature is gradually raised from 75-95 C. to 180-200 C. over a period of about 3-7 hours; in the final stage, the reaction temperature is maintained at ISO-200 C. for about 0.5-5 hours.

The manner of manipulating the reaction temperature during the first stage of the reaction in order to be in the 75-95 C. range for the beginning of the second stage of the reaction is not critical, e.g., an initial temperature of about -125 C. can be gradually lowered to 75-95 C. during the first stage of the reaction or the temperature can be maintained at 75-95 C. throughout the first stage of the reaction, etc. According to a particularly preferred embodiment of the invention, the reaction mixture is initially heated to -115 C. and maintained at a temperature gradually lowered to about 90 C. until about 25-45% conversion to polymer is obtained, after which the temperature is gradually raised to 180-200 C. over a period of about 3-7 hours and then maintained at ISO-200 C. for about 2-5 hours to complete the reaction. Especially good results are also obtained by initially heating the reaction mixture at 90 C. C. to about 25-35% conversion, then heating at a temperature gradually raised to 180-200 C. over a period of about 4-5 hours, and finally heating at 180-200 C. for 2-4 hours.

Although also generally useful as a new catalytic method of polymerizing styrene-type monomers, the present invention is particularly advantageous in that it permits the formation by a mass process of moldable polystyrenetype materials having lower residual monomer contents than the comparable polymers of the prior art. The reduced residual monomer content improves the physical and molding properties of the polymers.

It is obvious that many variations can be made in the products and processes set forth above without departing from the spirit and scope of this invention.

What is claimed is:

1. A process which comprises (1) dissolving a catalyst mixture consisting of:

(a) about 0.05-0.5 part by weight of a 1,2-diarylethane corresponding to the formula:

wherein R and R represent aryl radicals,

(b) about 0.00l-0.5 part by weight of an alpha-ketol corresponding to the formula:

RAM-R Bi /I wherein R represents a hydrocarbon radical, R represents a substituent of the group consisting of hydrogen and a hydrocarbon radical, and R" represents a substituent of the group consisting of hydrogen and a hydrocarbon radical,

(c) 0.05-1 part by weight of a monocarboxylic acid having a dissociation constant not higher than 1.0 10- at 25 C., and

(d) up to 0.1 part by weight of a peroxy compound of the group consisting of hydrogen peroxide and an organic peroxy compound having a half-life of at least 10 hours in benzene at 100 C.

in 100 parts by weight of a polymerizable material comprising at least a major proportion of a monovinyl aromatic monomer of the group consisting of a monovinyl aromatic hydrocarbon, an ar-halo monovinyl aromatic hydrocarbon, and mixtures thereof, and (2) heating to polymerize the polymerizable material.

2. A mass polymerization process which comprises (1) dissolving a catalyst mixture consisting of:

(a) about 0.05-0.5 part by weight of a 1,2-diarylethane corresponding to the formula:

R-CH -CH R' wherein R and R" represent aryl radicals,

7 (b) about 0.001-0.5 part by weight of an alpha-ketol corresponding to the formula:

OH RJHLR wherein R represents a hydrocarbon radical, R represents a substituent of the group consisting of hydrogen and a hydrocarbon radical, and R represents a substituent of the group consisting of hydrogen and a hydrocarbon radical,

(c) 0.05-1 part by weight of a monocarboxylic acid having a dissociation constant not higher than 1.0 10 at 25 C., and

(d) up to 0.1 part by weight of a peroxy compound of the group consisting of hydrogen peroxide and an organic peroxy compound having a half-life of at least 10 hours in benzene at 100 C in 100 parts by weight of a polymerizable material comprising at least a major proportion of a monovinyl aromatic monomer of the group consisting of a monovinyl aromatic hydrocarbon, an ar-halo monovinyl aromatic hydrocarbon, and mixtures thereof, (2) heating the polymerizable material at 75-125 C. until 15-45% conversion to polymer is obtained, the temperature being so regulated as to be in the 75-95 C. range when this conversion is obtained, (3) gradually raising the reaction temperature to 180200 C. over a period of about 3-7 hours, and (4) maintaining the reaction temperature at 180-200 C. for about 0.5-5 hours.

3. The process of claim 2 wherein the polymerizable material is styrene.

4. The process of claim 2 wherein the polymerizable material is a mixture of styrene and alpha-methylstyrene.

5. The process of claim 2 wherein the polymerizable material is a mixture of styrene and acrylonitrile.

6. The process of claim 2 wherein the polymerizable material is a mixture of styrene and methyl methacrylate.

7. The process of claim 2 wherein the polymerizable material contains a dissolved rubbery conjugated 1,3- diene polymer.

8. The process of claim 2 wherein the 1,2-diarylethane is 1,2-diphenylethane.

9. The process of claim 2 wherein the alpha-ketol is alpha-hydroxyacetophenone.

10. The process of claim 2 wherein the monocarboxylic acid is an alkanoic acid containing 12-20 carbon atoms.

11. The process of claim 2 wherein the catalyst mixture consists of (a) 0.05-0.1 part by weight of the 1,2- diarylethane, (b) 0.0010.l part by weight of the alphaketol, and (c) 0.1-0.6 part by weight of a monocarboxylic acid having a dissociation constant not higher than 1.0 10 at C.

12. The process of claim 2 wherein the catalyst mixture consists of (a) 005-01 part by weight of the 1,2- diarylethane, (b) 0.001-0.1 part by weight of the alphaketol, (c) 0.1-0.6 part by weight of a monocarboxylic acid having a dissociation constant not higher than 1.0 10- at 25 C., and (d) 0.0l0.1 part by weight of a peroxy compound of the group consisting of hydrogen peroxide and an organic peroxy compound having a halflife of at least 10 hours in benzene at C.

13. A mass polymerization process which comprises (1) dissolving a catalyst mixture consisting of (a) 005-01 part by weight of 1,2-diphenylethane, (b) 0.001-0.1 part by weight of alpha-hydroxyacetophenone, (c) 0.1-0.6 part by weight of stearic acid, and (d) 0.01-0.05 part by weight of di-t-butyl peroxide in 100 parts by weight of styrene, (2) heating the styrene to -115 C. and then gradually lowering the temperature to about 90 C. to obtain 25-45% conversion to polymer, (3) gradually raising the temperature to 220 C. over a period of about 3-7 hours, and (4) maintaining the reaction temperature at ISO-200 C. for 2-5 hours.

References Cited by the Examiner UNITED STATES PATENTS 2,675,362 4/54 Shusman 260-23 2,886,553 5/59 Stein et al 260880 3,066,115 11/62 Smith et al 260880 OTHER REFERENCES Orr et al., Can. J. Chem., 29 (1951), pages 949-58.

JOSEPH L. SCHOFER, Primary Examiner.

DONALD E. CZAJA, Examiner. 

1. A PROCESS WHICH COMPRISES (1) DISSOLVING A CATALYST MIXTURE CONSISTING OF: (A) ABOUT 0.05-0.5 PART BY WEIGHT OF A 1,2-DIARYLETHANE CORRESPONDING TO THE FORMULA: 